Preparation of conductive polyurethanes using a conductive quasi-solution

ABSTRACT

A conductive quasi-solution useful for making a homogeneously conductive single-phase polyurethane, comprising a transition metal salt, a carrier solution, and a dispersing agent, wherein said conductive quasi-solution has a transition metal salt concentration between 10 and 30% by weight, and methods of making thermoset and thermoplastic polyurethane polymers therewith.

BACKGROUND OF THE INVENTION

Certain applications of polymers require conductive, semi-conductive, orstatic charge-dissipating properties.

Electrically conductive polymer-products have been made by mixing anelectrically conductive material into the polymer during formation.Examples of such electrically conductive materials include powders suchas silver, copper, nickel, carbon black, and graphite; and ionizablemetal salts such as alkali metal tetraorganoborides. To providesatisfactory conductive properties, the amount of conductive powder in aconductive material can be as high as 10-40% by weight, which can affectthe thermal and mechanical properties of the polymer. Uniform highconductivity requires uniform distribution of the conductive materialthroughout the polymer bulk.

SUMMARY OF THE INVENTION

In one aspect, the invention features a conductive quasi-solution usefulfor making a homogeneously conductive single-phase polyurethane. Thequasi-solution includes between 10% and 30% by weight of a transitionmetal salt, a carrier solution, a dispersing agent. The carrier solutionincludes a polyol, a polyamine, or a flame retardant. In preferredembodiments, the carrier solution includes a flame retardant.

In another aspect, the invention features a method of making ahomogeneously conductive single-phase polyurethane, including the stepsof preparing a conductive quasi-solution and mixing an amount of theconductive quasi-solution with a diisocyanate and a polyurethaneprecursor to form a homogeneously conductive single-phase polyurethane(i.e., a solid solution). The polyurethane precursor is selected frompolyols and polyamines.

Mixing is accomplished according to either a conventional reactioninjection molding process, or a conventional thermoplastic polyurethaneproduction process.

The conductive thermoset and thermoplastic polyurethanes have manyapplications. Examples include coated integrated circuit boards, carbody parts, especially those which are to have a painted (baked)surface, such as bumpers and side panels; and durable carrying cases orother accessories in the electronics (e.g., computer) field for whichdissipation of static charge is desirable.

The transition metal salt provides conductive properties to thepolyurethane. As used herein, homogeneously conductive means thatconductivity is essentially uniform across the surface and throughoutthe volume of the bulk polyurethane, due to the uniform distribution offully-dissolved transition metal salts throughout the polymer. Thepolymer is thus a single-phase solid solution of polymer and dissolvedtransition metal salts, with an absence of transition metal saltparticles. The methods of the invention produce single-phase conductivepolyurethanes, which are therefore homogeneously conductive.

Other features and advantages of the invention will be apparent from thedetailed description, and from the claims.

DETAILED DESCRIPTION OF THE INVENTION

The invention generally features the use of a conductive quasi-solutionto make a homogeneously conductive, single phase polyurethane. Theconductive quasi-solution is a dispersion including a transition metalcation, a dispersing agent, and a carrier. A conductive quasi-solutionhas both dissolved and undissolved transition metal salt, the maximumdiameter of undissolved particles being 0.5 μm, and preferably 0.1 μm.

The invention resides, in part, in the discovery that a quasi-solutionof transition metal salts will produce a conductive single-phasepolyurethane product. This product, whether formed by reaction injectionmolding or conventional thermoplastic polyurethane production, is asolid solution, rather than a dispersion of undissolved transition metalsalts in the polymer. Upon mixing, the undissolved transition metalparticles dissolve into the forming polymer. For example, mixing acopper (II) chloride quasi-solution (a brown dispersion with undissolvedcopper salt particles) with the urethane precursor(s) results in aclear, dark green solution without any precipitated or undissolvedcopper salt particles. Similarly, mixing an iron (III) chloridequasi-solution (a dark grey dispersion) with the urethane precursor(s)results in a clear, light brown solution without any precipitated orundissolved particles of iron salt. The reaction of the precursor with adiisocyanate forms a uniform, light green polyurethane product where acopper quasi-solution is used; a uniform light brown polyurethaneproduct is formed where an iron quasi-solution is used. These colorchanges indicate that the polyurethane product is a solid solution,i.e., a homogeneous, single-phase polymer.

In addition, the transition metal cations form d-orbital complexes withnucleophilic oxygen (i.e., carbonyl) and nitrogen atoms. Such complexesform bridged networks between different polyurethane polymer molecules,which improves uniformity and conductivity.

Transition Metal Salt

A transition metal salt is capable of carrying or conducting an electriccharge. According to the invention, a transition metal salt includes atransition metal cation and one or more counter-anions to form a neutralsalt. Each counter-anion may be any anion that does not interfere withthe homogeneity or semi-conductivity of the final polymer product.Examples of transition metal cations include Cu (II), Co (II), Zn (II),Ni (II), Fe (II), and Fe (III). Fe (III) and Cu (II) are preferred.Examples of counter-anions include fluoride, chloride, bromide, iodide,cyanide, thiocyanate, acetate, lactate, phosphate, and tartrate.Thiocyanate, bromide, chloride, and acetate are preferred. Thus,examples of transition metal salts include CuCl₂, CuBr₂, Cu(CH₃ COO)₂,Cu(SCN)₂, FeBr₃, Fe(SCN)₃, FeCl₂, CuCl₂, and Fe(CH₃ COO)₃. Transitionmetal salts are available commercially from, e.g., Aldrich Chemical Co.(Milwaukee, Wis.).

The conductive quasi-solution preferably has a transition metal saltconcentration (w/w in carrier and dispersing agent) of between 10 and30%, and more preferably between 15 and 25%. Generally, in the absenceof a dispersing agent, the solubility of a transition metal salt in acarrier is between 5 and 10% (w/w). The concentration (w/w) oftransition metal salts in the final product is between 0.02 and 1.0%,and is preferably between 0.04 and 0.2% (see, e.g., Example 12). Thus,the mole percent of transition metal salts in the final product isbetween 1.52×10⁻⁴ and 7.4×10⁻³ mole percent, and preferably between3.0×10⁻⁴ and 1.5×10⁻³ mole percent. In some embodiments, more than onetransition metal salts are used; as a result, more than one transitionmetal cation or more than one counter-anion is present in the conductivequasi-solution.

Carrier Solution

According to the invention, a carrier solution is one or more organicsolvents, the combination solution being stable at high temperature.Such a temperature-stable non-aqueous liquid is characterized by a highboiling point and a low vapor pressure. A high boiling point is aboiling point of at least 350° F., and preferably at least 500° F. A lowvapor pressure is a vapor pressure of no more than 50 mm Hg at 110° C. Alow vapor pressure is also characterized by the visual absence of whitesmoke at 300° F. Examples of carrier solutions include flame retardantssuch as tri(haloalkyl)phosphates, and preferablytri(chloro-ethyl)phosphate ("Fyrol® CEF," Akzo Chemical Corp., Chicago,Ill.) and tri(β-chloroisopropyl)phosphate ("PCF"); polyamines such asPolamine® 650, Polamine® 1000, and Polamine® 2000 (Air Products,Allentown, Pa.); and polyols such as polypropylglycol ("PPG"),Terathane® 650, Terathane® 1000, Terathane® 2000, Terathane® 2900,Terathane® CL-2000 (Du Pont de Nemours, Wilimington, Del.), andPluracol® Polyol 924, Pluracol® Polyol 538, and Pluracol® Polyol 774(BASF Corp., Parsippany, N.J.), and butanediol XB (GAF Corp., Wayne,N.J.)

In some embodiments, more than one solvent is present in the conductivequasi-solution, such as the following carrier combinations: a polyol anda polyamine; two polyols; two polyamines; a flame retardant and apolyol; a flame retardant and a polyamine; or a flame retardant, apolyol, and a polyamine.

Dispersing Agent

According to the invention, a dispersing agent is a non-ionic surfactantwhich acts to stabilize the metal salt in the conductive quasi-solutionbefore use in a reaction injection molding process. After mixing, thedispersing agent also improves solubility of the transition metal salt,improves uniform mixing, and thus improves the conductive homogeneity ofthe final product. Stabilization of the conductive quasi-solutionincludes increasing the solubility of the transition metal salt withoutincreasing the percent of carrier. Examples of dispersing agents includeDC 190 and DC 193 (Dow Corning Corp., Midland, Mich.), DABCO™ DC 5418(Air Products Co.) and RC Dispersant WM (Rhein Chemie Corp., Trenton,N.J.). Dispersing agents are present in the quasi-solution at aconcentration between 0.5 and 5%, and preferably 1 and 3% (w/w).

Mixing Process

The conductive quasi-solution of the invention may be used in either atwo stream process (streams A and B) or a three stream process (streamsA, B, and C) to produce a molded homogeneously conductive polyurethaneform. The mixing step may be part of either a conventional reactioninjection molding process or a conventional production method of makingthermoplastic polyurethane. A diisocyanate can be in prepolymer form(i.e., partially cured with a polyol or polyamine) or pure form, such asmethylene diisocyanate (MDI) or toluene diisocyanate (TDI) (BASF Corp.).

In a two stream process, stream A includes a diisocyanate in either aprepolymer form such as the commercially available Bayflex® 110-25A(Bayer Corp, Pittsburgh, Pa.) or pure form, such as Isocyanate® 76 andIsocyanate® 227 from BASF. Stream B includes a conductive quasi-solutionat a concentration between 0.2 to 2.0% by weight, and a polyurethaneprecursor such as a polyol or a polyamine in a solvent such as Bayflex®110-35B, IMR (Bayer Corp.). Stream B also may include a catalyst such asan amine catalyst, a tin catalyst, or a bismuth catalyst, in aconcentration between 0.01 and 0.5%, and preferably between 0.02 and0.3% by weight with respect to the total amount of polyol and polyamine.Examples of catalysts include DABCO™ 33-LV, DABCO™ T-12 and DABCO™ T-9(Air Product Co.) and Fomrez® UL-32 (Witco, New York, N.Y.).

In a three stream process, stream A includes a diisocyanate as above.Stream B includes a polyurethane precursor such as a polyol or apolyamine. In general, the total concentration of polyol and polyamineis at least 95%, the remainder being additives such as lubricants (e.g.,internal mold release materials), catalysts, pigments, mineral additives(e.g., glass fibers, iron oxide, carbon black, or graphite). Stream Cincludes the conductive quasi-solution. Stream C may also includeadditives such as pigment.

In either process, the streams are mixed at a specified flow rate ratio,temperature, and pressure at the mixing head and rapidly injected intothe mold, e.g., within 1 or 2 seconds. A person of skill in the art willeasily be able to determine the specific ratios, temperatures, andpressures to be used. See, e.g., Example 12.

In general, the conductive quasi-solution of the invention has a veryshort pot life (e.g., less than 5 seconds). After contact with apolyurethane precursor such as a polyol or a polyamine or a combinationthereof, the previously-undissolved transition metal salt particles inthe conductive quasi-solution completely dissolve. Moreover, once thestreams are in contact with each other, a single-phase solid solutionpolyurethane is formed. The concentration (w/w) of the quasi-solution inthe final product is between 0.1 and 5% and preferably between 0.2 and1.0%.

Without further elaboration, the present invention can be utilized toits fullest extent based on the description herein. The followingspecific examples are offered by way of illustration, and not by way oflimitation.

EXAMPLES Example 1

Fyrol CEF (tri-(β-chloroethyl)phosphate (2475 g, Akzo Corp, Chicago,Ill.) was added to a four liter flask. RC Dispersant WM (125 g, RheinChemie Corp., Trenton, N.J.) was slowly added to the Fyrol® CEF withmechanical stirring (400 rpm), followed by slow addition of 650 g ofCuCl₂ (Aldrich Chemical, Milwaukee, Wis.) over a period of 6 hours withmechanical mixing at 150° F. A uniform, conductive quasi-solution wasformed, having a transition metal salt concentration of 20% by weight.

Example 2

Procedure according to Example 1, except 650 g of FeCl₃ was added,instead of 650 g CuCl₂.

Example 3

Procedure according to Example 1, except 325 g of FeCl₃ and 325 g CuCl₂were added, instead of 650 g CuCl₂.

Example 4

Procedure according to Example 1, except tri(β-chloroisopropyl)phosphatewas added instead of (tri-(β-chloroethyl)phosphate.

Example 5

Procedure according to Example 1, except a polyol solution was addedinstead of Fyrol® CEF, for use in RIM.

Example 6

Procedure according to Example 1, except a polyamine solution was addedinstead of Fyrol® CEF, for use in RIM.

Example 7

Procedure according to Example 1, except a solution including bothpolyamine and polyol was added instead of Fyrol® CEF, for use in RIM.

Example 8

Procedure according to Example 1, except a thermo-plastic polyolsolution was added instead of Fyrol® CEF, for use in making athermoplastic polyurethane.

Example 9

Procedure according to Example 1, except a thermo-plastic polyaminesolution was added instead of Fyrol® CEF, for use in making athermoplastic polyurethane.

Example 10

Procedure according to Example 1, except a solution including bothpolyamine and polyol was added instead of Fyrol® CEF, for use in makinga thermoplastic polyurethane.

Example 11

Procedure according to Example 1, except one or more transition metalsalts selected from CuBr₂, Cu(CH₃ COO)₂, Cu(SCN)₂, FeBr₃, Fe(CH₃ COO)₃,Fe(SCN)₃ FeCl₃, and CuCl₂.

Example 12

Bayflex® 110-35A, part A, and Bayflex® 110-35B,IMR or Bayflex® 110-35B,part B were obtained from Bayer Corp., Pittsburgh, Pa. The conductivequasi-solution of Example 1 was premixed with part B to form aconductive polyurethane precursor solution. An Admiral 2640-2 highpressure, high temperature RIM machine was used to form a plaque havinga transition metal salt concentration in the final product of 0.25%,0.50%, and 0.75%.

The process parameters were as follows: 2.0 lb/sec injection rate, 1.20sec injection time, 45 sec cure time, Part A (diisocyanate) temperature125° F., Part B (polyol or polyamine) temperature 135° F., 155° F. moldtemperature, 1980 psi mix pressure for part A, 1920 psi mix pressure forpart B, tank pressures for both A and B were 24 psi. The plaque size was22" by 28". A ChemTrend® 2006 mold release, zinc stearate aqueoussolution wash soap was used. The plaque was cured at 250° F. for 1 hourand washed with the zinc stearate soap. Electrical paint was applied at85 kV with a gun speed of 30 ips. A superior, uniform paint coat wasachieved (see Table I).

                                      TABLE I                                     __________________________________________________________________________    Physical Properties of Plaque                                                 MPC Specif.                                                                            Tensile                                                                            Flexural                                                                            Elongation                                                                              Resistivity                                     con.                                                                              gravity                                                                            strength                                                                           modulus                                                                             (%)       ohm-cm                                                                             ohm/sq                                     (%) (g/cc)                                                                             (psi (ksi) Parallel                                                                           Perpend                                                                            volume                                                                             surface                                    __________________________________________________________________________    .00 1.21 2808 103.6 108  134  4.9E13                                                                             2.9E15                                       .25    1.17      2719      92.1        89       122  4.3E11     2.7E12                                          .50    1.15      2690      90.7                                               89       114  8.4E10     6.2E11                                               .75    1.17      2876      87.5                                               93       113  2.2E10     1.6E11                                               1.8                                                                                         5.0E8       2.8E10          __________________________________________________________________________

Example 13

Procedure according to Example 12, except the following was used: part A(Bayflex® 110-25A); part B (Bayflex® 110-25B premixed with a conductivequasi-solution having a 10% by weight Cucl₂ transition metal saltconcentration). The mixing time was 1.2 seconds at 150° F.; the materialwas postcured for 1 hour at 260-270° F., and then electrically paintedto yield a uniform paint coat with an excellent appearance and goodfastness (see Table II).

                                      TABLE II                                    __________________________________________________________________________    Physical Properties of Plaque                                                     MPC                                                                              Bayflex                                                                            Volume                                                                             Surface   Tensile                                                                            Tear                                            Sold   addi  110-25B  resist    resist    Hardness strength str.  Elong       (%)     (g)    (g)    (ohm-cm) (ohm/sq)  (D)       psi     pli              __________________________________________________________________________                                       (%)                                        0   0  100   5.0E12                                                                            2.0E13                                                                             45D  2460 408                                                                              187                                          1.2    1.8     100     2.0E9    1.1E11      53D       3110   405    214       3.1    4.6     100     5.0E8    8.0E10      50D       2888   337    160       6.1    9.0     100     1.5E8    6.0E10      47D       2351   346    103       16.2   24.0    100     6.9E7    2.3E10      37D       1670   276            __________________________________________________________________________                                       87                                     

Example 14

Thermoplastic polyurethane (TPU) is made by mixing a conductivequasi-solution (0.1 to 10%) into a polyol or polyamine to form aconductive precursor solution. The precursor solution is reacted withpure diisocyanate at a temperature between 100 and 240° F. to formthermoplastic polyurethane. The polyurethane material is completelycured at 200° F. for 12 hours and cooled to room temperature. Aftercooling, the material is extruded and formed into pellets for packing.The urethane product is semiconductive, and useful for static chargedissipation with a volume resistivity between about E8 and E10 ohm-cm.

OTHER EMBODIMENTS

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method of making a homogeneously conductivesingle-phase thermoplastic polyurethane, comprisingmixing, with heating,a combination containing a transition metal salt, a dispersing agent,and a solvent comprising a flame retardant, a polyol, or a polyamine toprovide a conductive quasi-solution having undissolved particles of saidtransition metal salt in said solvent, and combining said conductivequasi-solution with a thermoplastic polyurethane precursor and adiisocyanate to provide a homogeneously conductive single-phasethermoplastic polyurethane containing said transition metal salt.
 2. Themethod of claim 1, wherein said transition metal salt comprises atransition metal selected from Cu (II), Fe (III), Ni (II), Zn (II), andCo (II), and a counter-anion selected from acetate, tartrate, lactate,phosphate, oxalate, fluoride, chloride, bromide, iodide, thiocyanate,and cyanide.
 3. The method of claim 2, wherein said transition metalsalt comprises Fe (III) or Cu (II).
 4. The method of claim 2, whereinsaid transition metal is Cu (II) or Fe (III), and said counter-anionsare independently selected from acetate, thiocyanate, chloride, orbromide.
 5. The method of claim 1, wherein there are at least twotransition metal salts in said conductive quasi-solution.
 6. The methodof claim 5, wherein said transition metal salts comprise Fe (III) and Cu(II).
 7. The method of claim 5, wherein said transition metal saltcomprises copper chloride.
 8. The method of claim 1, wherein saidcombination contains between 10% and 30% by weight of said transitionmetal salt.
 9. The method of claim 1, wherein said combination containsbetween 15% and 25% by weight of said transition metal salt.
 10. Themethod of claim 1, wherein said dispersing agent comprises a non-ionicsurfactant.
 11. The method of claim 1, wherein the concentration of saiddispersing agent in said conductive quasi-solution is between 0.5% and5% by weight.
 12. The method of claim 1, wherein the concentration ofsaid dispersing agent in said conductive quasi-solution is between 1%and 3% by weight.
 13. The method of claim 1, wherein said solventcomprises a flame retardant comprising a phosphate haloalkyl ester or adiphosphate haloalkyl ester.
 14. The method of claim 1, wherein saidsolvent comprises a polyol.
 15. The method of claim 1, wherein saidsolvent comprises a polyamine.
 16. The method of claim 1, wherein saidsolvent comprises a combination of a polyol and a polyamine.
 17. Themethod of claim 1, wherein said combining step includescombining saidconductive quasi-solution with a thermoplastic polyurethane precursor toprovide a conductive thermoplastic polyurethane precursor, and combininga first stream comprising said conductive thermoplastic polyurethaneprecursor and a second stream comprising said diisocyanate to providethe homogeneously conductive single-phase thermoplastic polyurethane.18. The method of claim 17, wherein said transition metal salt is fullydissolved in said conductive thermoplastic polyurethane precursor. 19.The method of claim 17, wherein said quasi-solution in said conductivethermoplastic polyurethane precursor is about 0.1 to 10% by weight. 20.The method of claim 17, wherein said first stream is combined with saidsecond stream at a temperature between 100 and 240° F.
 21. The method ofclaim 1, further comprising postcuring the thermoplastic polyurethaneafter the combining step.
 22. The method of claim 17, wherein saidconductive thermoplastic polyurethane precursor contains an aminecatalyst, a tin catalyst, or a bismuth catalyst.
 23. The method of claim22, wherein said catalyst is between 0.01 and 0.5% by weight withrespect to the total amount of said thermoplastic polyurethaneprecursor.
 24. The method of claim 22, wherein said catalyst is between0.02 and 0.3% by weight with respect to the total amount of saidthermoplastic polyurethane precursor.
 25. The method of claim 1, whereinsaid homogeneously conductive single-phase thermoplastic polyurethanecontains between 0.02% and 1% of the transition metal salt by weight.26. The method of claim 1, wherein said homogeneously conductivesingle-phase thermoplastic polyurethane contains between 0.04% and 0.2%of said transition metal salt by weight.
 27. The method of claim 1,wherein said undissolved particles have a maximum diameter of from about0.1 μm to about 0.5 μm.